The production of phenol from cyclohexylbenzene is an emerging technology, interesting in that it co-produces cyclohexanone, rather than acetone. In this process, cyclohexylbenzene is first oxidized to form hydroperoxide thereof, which is then cleaved in the presence of an acid catalyst to obtain phenol and cyclohexanone.
Cyclohexylbenzene may be produced, for example, by direct alkylation of benzene with cyclohexene, or by hydroalkylation of benzene. In the latter process, benzene reacts with hydrogen in the presence of a catalyst such that the benzene undergoes partial hydrogenation to produce a cyclohexene intermediate, which then alkylates part of the benzene starting material. In this regard, U.S. Pat. No. 6,037,513 has disclosed that cyclohexylbenzene selectivity in the hydroalkylation of benzene can be improved by contacting the benzene and hydrogen with a bifunctional catalyst comprising of at least one hydrogenation metal and a molecular sieve of the MCM-22 type. The hydrogenation metal is preferably selected from palladium, ruthenium, nickel, cobalt, and mixtures thereof and the contacting step is conducted at a temperature of about 50° C. to 350° C., a pressure of about 100 kPa to 7000 kPa, a hydrogen to benzene molar ratio of about 0.01 to 100 and a weight hourly space velocity (WHSV) of about 0.01 hr−1 to 100 hr−1. This reference discloses that the resultant cyclohexylbenzene can then be oxidized to the corresponding hydroperoxide and the peroxide decomposed to the desired phenol and cyclohexanone. Nonetheless, notwithstanding the high selectivity of the hydroalkylation reaction over the MCM-22 molecular sieve-based bifunctional catalyst in the disclosed method, small amounts of cyclohexane and methylcyclopentane are produced in the hydroalkylation effluent.
The overall benzene conversion rates in the hydroalkylation reaction are typically only 40 wt % to 60 wt %. Therefore, recycle of unreacted benzene is desired. Unless removed, impurities including cyclohexane and methylcyclopentane will tend to build up in the recycle benzene stream thereby displacing benzene and increasing the production of undesirable by-products. Thus, a problem facing the commercial application of cyclohexylbenzene as a phenol precursor is removing the cyclohexane in the benzene recycle streams.
In addition, benzene hydroalkylation is known to produce a non-negligible amount of di-cyclohexylbenzenes and tri-cyclohexylbenzenes, which are typically converted to cyclohexylbenzene via transalkylation with benzene to increase the overall cyclohexylbenzene yield of the process.